Conventionally, in an injection locking type of laser device in which seed laser light oscillated from an oscillator is amplified in an amplifier, an art of synchronizing light emission of seed laser light and light emission of amplified laser light in the amplifier is disclosed in, for example, Japanese Patent Laid-open No.2000-156535. According to Japanese Patent Laid-open No.2000-156535, the seed laser light emitted from a titanium sapphire laser device is amplified by amplification discharge inside an amplifier chamber, and is emitted as amplified laser light. The art disclosed in the aforementioned Laid-open Patent uses a harmonic component of the band-narrowed titanium sapphire laser device as an oscillator. However, the harmonic component of the titanium sapphire laser device produces very low output energy, and in order to obtain seed laser light having sufficient output energy, which can be amplified in the amplifier, the titanium sapphire laser device becomes large in size and expensive.
When an excimer laser device is used as a lithography light source, a center wavelength of amplified laser light sometimes has to be changed according to ambient air pressure and the like. This needs changing a center wavelength of the seed laser light, but it is difficult when the oscillator is a titanium sapphire laser device. Further, when a fluorine molecular laser device is constituted to be of an injection locking type, the center wavelength thereof is shorter than an ArF excimer laser device (157 nm), and therefore it is difficult to find a laser device suitable as an oscillator. Consequently, as a light source for lithography, an injection locking type of laser device with a discharge excitation type of excimer laser device or fluorine molecular laser device, which is the same as the amplifier, being used as an oscillator is used.
FIG. 18 shows a constitution of an injection locking type of fluorine molecular laser device using the discharge excitation type of fluorine molecular laser device as an oscillator, according to a prior art. In FIG. 18, an oscillator 11A includes an oscillator chamber 12A in which a laser gas containing fluorine and neon (Ne) is sealed. A pair of oscillator electrodes 14A and 15A are placed at a predetermined position of the oscillator chamber 12A to oppose each other. The oscillator 11A includes an oscillator charger 42A to output oscillator voltage VA. It also includes an oscillator discharge circuit 43A for pulse-compressing the oscillator voltage VA and transferring it between the oscillator electrodes 14A and 15A to cause pulse discharge.
An amplifier 11B includes an amplifier chamber 12B in which a pair of amplifier electrodes 14B and 15B are placed to oppose each other and a laser gas is sealed. Further, it includes an amplifier charger 42B to output amplifier voltage VB, and an amplification discharge circuit 43B for pulse-compressing the amplifier voltage VB and transferring it between the amplifier electrodes 14B and 15B to cause pulse discharge. The oscillator voltage VA and the amplifier voltage VB are collectively called charge voltages VA and VB.
When a trigger signal G is outputted to a laser controller from an aligner 25 such as a stepper, discharge is caused between the oscillator electrodes 14A and 15A to excite laser gas, and seed laser light 21A in a pulse form occurs. The seed laser light 21A is oscillated with bandwidth of wavelength being narrowed by a band-narrowing unit 30. The amplifier 11B outputs a trigger signal G3 by delaying the trigger signal G by a predetermined delay time to be taken by a delay circuit 44 to cause amplification discharge between the amplifier electrodes 14B and 15B. As a result, the seed laser light 21A is amplified with a center wavelength λc and a spectral bandwidth Δλ (hereinafter, they are called wavelength characteristics) being kept while traveling between unstable resonators 36 and 37 to be amplified laser light 21B and is emitted.
However, the aforementioned prior art has the disadvantages described below. Specifically, the oscillator discharge circuit 43A and the amplification discharge circuit 43B have LC resonator circuits for pulse compression, and magnetic cores contained in the LC resonator circuits each have the characteristic that a voltage-time product is fixed. Consequently, in each of the oscillator 11A and the amplifier 11B, time from the input of the trigger signal G to the occurrence of discharge between the electrodes 14 and 15 varies for each pulse oscillation due to variations in high voltages VA and VB. A short-term time variation as described above is called jitter.
Specifically, the time from the trigger signal G to the light emission of the seed laser light 21A in the oscillator 11A and the time from the trigger signal G to the amplifier 11B causing amplification discharge are varied independently. As a result, the time from the trigger signal G to the emission of the amplified laser light 21B is varied in a short-term, which sometimes causes a problem to working. Further, a timing of light emission of the seed laser light 21A and a timing of amplification discharge are not matched with each other, and the seed laser light 21A is not suitably amplified, whereby the disadvantage that the output energy, the center wavelength λc, the spectral bandwidth Δλ or the like of the amplified laser light 21B is varied.